Writer Viet Thanh Nguyen spent five years bringing “The Sympathizer” to the screen, but it wasn’t until a recent cruise down a California freeway that he realized what a big deal the HBO adaptation of his Pulitzer-winning novel truly is.

“I was driving on the Hollywood Freeway with my family, and my son said, ‘Look, there’s a billboard with “The Sympathizer” on it!’ ” Nguyen said ahead of the limited series recent premiere on HBO and streaming service Max.

“We immediately pulled over, thankfully, to a safe place, and everybody spilled out of the car to take pictures with a billboard,” he says. “And you don’t do that with a book. Books don’t get billboards, usually.

“That’s just an example of how vast the scale is, that you can drive on a freeway through LA now and literally see gigantic billboards with the whole cast’s faces. And that’s amazing. Absolutely amazing.”

“The Sympathizer” is the story of the Captain, a South Vietnamese spy for the North Vietnamese during the Vietnam War, a man of two minds, as he says of himself in the novel, whose communist leanings push against his fondness for the United States, where he’d studied before the war. The seven- episode limited series follows the Captain from the fall of Saigon to his journey to the U.S. and eventual return to Vietnam. Its cast consists almost entirely of actors of Vietnamese origins. Most, such as Australian actor Hoa Xuande, who plays the Captain, are unfamiliar to American audiences, though some will be familiar — such as the acclaimed actor Kieu Chinh, who plays the Major’s Mother, and “Paris By Night” emcee Ky Duyen, who plays the General’s Wife.

“The story is about refugees, a traitor, heroes, a spy, and love and relationships,” says Chinh, 86. “This is the first time a Vietnamese novel is brought to the screen, and most of the characters are played by Vietnamese for the first time.”

Sandra Oh and Robert Downey Jr. also star in the series, with Oh playing university secretary Ms. Mori, and Downey, playing four different characters — a CIA agent, a professor, a filmmaker and a congressman — who are antagonists of the Captain in the series.

Part black comedy, part spy thriller, “The Sympathizer” was co-created by Canadian writer-producer Don McKellar and South Korean writer-director Park Chan-wook.

Nguyen’s debut novel was a literary sensation on publication, earning acclaim for its subversion of genre tropes, such as spy novels and war stories, while telling a serious, entertaining and often funny story from the point of view of the Vietnamese side of the war.

After it won the 2016 Pulitzer Prize for fiction, Nguyen set about seeking a home for the story in Hollywood. In 2021, A24 optioned it as a series for HBO, with other producers — including Team Downey, Robert and Susan Downey’s production company — coming on board.

Nguyen served as an executive producer on the project. McKellar joined as showrunner after Nguyen mentioned he thought Park Chan-wook would be a dream director, and a fellow producer who knew McKellar had written a script with the South Korean filmmaker, reached out to McKellar.

He also mentioned Oh as a possible choice for Ms. Mori, and McKellar, a close friend of the former “Grey’s Anatomy” star, reached out and got her on board.

To the writer, spending time with producers, cast and crew on set and location left Nguyen in awe of the work that went into making his book into a thrilling spectacle of a series.

“I mean, it literally involves hundreds of people working well over a year at a huge cost to make this, whereas I wrote the whole thing sitting in a little room by myself,” Nguyen says.

“Reading and watching are very different experiences and very hard to compare. But they’re both immersive in their own ways. The process of interacting with someone’s words, but then conjuring, in my own mind, whatever’s happening is quite different than sitting more passively in front of a screen.

“But when the screen experience works, it can be really incredible, and I think it does work in this series.”

And the literary world seems awed by the adaptation, too, Nguyen says.

“The degree of excitement that this TV series has generated amongst book people is interesting,” he says. “It’s a little bit humbling, like, ‘OK, well, I did publish a book, and people were excited about that.’ But not at this level.”

While much of the cast was found through a global search of the Vietnamese diaspora, the two primary female actors in this story were found much closer to Hollywood: Both are residents of Huntington Beach, California.

Chinh laughs when she’s asked how she came to be cast in the series. Shortly after “The Sympathizer” was published, she went to Irvine, California, to a book event for Nguyen and the author recognized her in the audience.

“At that time, he doesn’t know that the book will turn to on-screen,” Chinh says. “So he just says, ‘Oh my God, we have the legendary actress Kieu Chinh in the audience.’ And he said, ‘Hopefully one day if the book turns into a series, you must be one of the characters.’ ”

Flash-forward five or six years, Chinh and Nguyen are friends, and one day her manager calls her to a meeting with McKellar and Chan-wook.

“We just talked a little bit and they gave me the part,” she says.

Duyen, after 30 years as host of the musical variety show “Paris By Night,” wanted to try something new. Through her friendship with Chinh, she was referred to an agent. A week or so later, the agent asked her to do a self- recorded audition for “The Sympathizer.” A Zoom audition with Chan-wook soon followed.

“I thought, ‘OK, it’s probably several months that we hear whether or not” she got the part, Duyen says. “An hour later, my agent told me you got the role, and I started to realize how big this thing is.”

As a prestige TV series, “The Sympathizer” is made to entertain, and it does that with the multilayered storylines that stretch from the Captain’s present into his future and his past.

But the series also presents a fresh and unfamiliar perspective on the war, that of the Vietnamese people rather than that of American soldiers, as has been seen in films like “Platoon,” “Apocalypse Now” and “Full Metal Jacket.” By showing the perspective of the Vietnamese people, whose lives and land were torn apart by the war, it can’t help but educate viewers, too, those involved in the project say.

“I think that this war was unique,” McKellar says. “The first case, but I think still the only real case, where our conception of the war is through the movies. So this show, the first thing it’s doing is saying, ‘OK, Americans, OK, world, let’s look at this from the other side,’ and remind yourself that it was on Vietnamese soil. That the people who suffered most and the people who suffered longest were the Vietnamese people.

“Which isn’t to say that Americans didn’t suffer. They did. But it’s saying, ‘Sympathize with this other side. Put yourself in the other side.’ And then recognize that side also has divisions and also has complexity, and that is much more complicated than you think.”

Just as “Platoon” and other American movies shaped impressions of the Vietnam War in the ’70s and ’80s, so will “The Sympathizer” shape views of it today, Nguyen says.

“For better and for worse, this TV series will not just be an entertainment, but also function as a history lesson for many, many people,” he says. “This will be their first exposure to the war in general, and for those who know anything about the American perspective, it’ll be their first exposure to any Vietnamese perspective.”